Melissa A. Vandiver

Mechanical testing of small, thin samples in a humidity-controlled oven

A new fixture for the mechanical characterization of thin polymer films under controlled temperature and relative humidity conditions is reported. Novel conducting polymers are often synthesized in small quantities and processed into films on the order of 10–100 microns thick. Standard tensile tests do not allow for adequate testing of these small sample sizes. Hence, a modification of the Sentmanat Extensional Rheometer (SER) to perform tensile testing on thin membranes is presented. Since the standard L-shaped pins do not secure thin polymer films at lower temperatures (i.e., below the melting point), screw down clamps were created to allow for mechanical characterization of solid polymer films. The new testing apparatus allows for mechanical characterization with as little as 2 % of the material needed for testing on a traditional tensile tester. In a parallel effort, a humidity delivery system developed for the TA Instruments ARES-G2 rheometer allows for testing at a range of temperatures (30–100 °C) and relative humidity conditions (0–95 % RH). The novel oven was benchmarked with low density polyethylene and Nafion 115Ⓡ. While the new experiment was built for characterization of ion exchange membranes for fuel cells, the oven is capable of characterizing any environmentally sensitive material using all standard rheometer geometries.

Designing Alkaline Exchange Membranes from Scratch

Abstract : There is increasing interest in the alkaline exchange membrane (AEM) fuel cells as this device, if realized, could allow the use of inexpensive metal catalysts and the oxidation of a variety of convenient liquid fuels. While there have been some dramatic early achievements, there is still a need for a fundamental study of anion transport, cation stability and the formation of robust thin films in this area. We have undertaken a comprehensive study of AEMs where theory is linked to well-defined model systems, both in solution and in the solid state, which are characterized using very careful environmental control such that the models can be validated and used predictively. We are also fabricating a number of random copolymer AEMs that can be produced readily in large quantities, allowing us to understand film formation coupled with transport and stability. Those based on perfluorinated backbones invite interesting comparisons with the analogous proton exchange membranes.